1. Field of the Invention
The present invention relates to antenna and antenna array, and more particularly, to a dual notch antenna and antenna array thereof efficiently increasing the impedance bandwidth.
2. Description of the Related Art
Typically, most of vehicle radar system applies a microstrip antenna array, with a wireless signal transceiver of the vehicle radar system disposed inside a vehicle bumper or a fan guard. The vehicle radar system transmits and receives millimeter-wave wireless signal for carrying out application such as distance detection or information exchange. Because a vehicle bumper is usually provided with a shock absorbing Styrofoam or fiberglass therein, the internally available space is limited. As a result, the radar signal is easily attenuated, causing a designing difficulty of the antenna array.
Also, typical vehicle radar system operates in a frequency band between 24 GHz to 77 GHz. Increasing the antenna performance and raising the antenna gain at a high frequency is difficult. In addition, the available space limitation is to be considered. Therefore, the difficulty of the antenna designing is increased.
Furthermore, US2014/0145909A1 discloses an antenna and array antenna, comprising a radiation member; a grounding element forming an area, wherein the radiation is disposed in the area, and an opening is formed near the fourth side of the radiating element; an extending bar, electrically connected to the fourth side of the radiating element, and extended toward the opening of the grounding element; a first connection element, having one terminal connected to the first side and the fourth side of the radiating element, and another terminal electrically connected to the grounding and feed-in element; and a second connection element, having one terminal electrically connected to the third side and the fourth side of the radiating element, and another terminal electrically connected to the grounding and feed-in element.
The fourth side of the radiation element above is provided with a concave structure and electrically connected with the extending bar. However, as shown by the reflection coefficient frequency response diagram, the effective bandwidth of the antenna at a frequency about 24 GHz is not optimal, failing to achieve a preferably impedance match for avoiding the signal reflection. Also, the fourth side of the radiation has a concave structure. In the basic antenna theory, relative structural design has been mentioned for increasing bandwidth. However, such structure is not suitable for antenna array.
Therefore, it is desirable to increase the antenna efficiency and impedance bandwidth thereof.